Increasing the yield of gasoline boiling range product from heavy petroleum stocks



Feb. 27, 1962 c. H. WATKlNS 3,023,158

INCREASING THE YIELD OF GASOLINE BOILING RANGE PRODUCT FROM HEAVYPETROLEUM STOCKS Filed March 21, 1960 Charge Stoc/r I l HydrogenHydrorefining Zone 5 7 NH3 f SeparoI/on 7 Zone v n s 6 26 :9 H Light,Gaseous Hydrocarbons Aromatic Extracting Zone /2 -/4 '26 /3\ I //5Extract Raff/note Recovery Recovery Zone Zone Hi h Boi/in /6\ Grac%edPro act /77 Hydrogen /8 fag Hydrocrac/ring gf g I Zone Zone,

20 3/ 2/ f 32 Separation Separation 7 Zone 1 Zone Light Gases LightGases liVVE/VTOR: 27 v 25 Char/es H, Watkins I i B).- Jet Fuel ProductsGasoline Products 5% A rromvgys 3,023,158 IN CREAING TIE YIELD FGASOLINE BQILHJG RANGE PRGDUCT FRSM HEAVY PETROLEUM SEOCKS Charies H.Watkins, Arlington Heights, ill, assignor to Universal Gil XQHS Company,Des Plaines, 11L, a corporation of Delaware Filed Mar. 21, was, Ser. No.16,312 9 Claims. (Ci. 20889} This invention relates to a process forconverting high boiiing hydrocarbon stocks into a gasoline boiling rangeproduct by a combination process in which each of the several stages arepeculiarly adapted to convert the particular class of components presentin the charge stock into desirable gasoline components, effecting suchconversion of the separated components at the most economical andpractical conditions suited to these components. More specifically, thisinvention relates to a combination process in which the aromaticcomponents of a high boiling petroleum fraction are recovered therefromand separately hydrocracked in a process involving a catalystparticularly adapted to the conversion of the aromatic components andseparately converting the parafinic, aliphatic components of the feedstock in a catalytic cracking stage and at conversion conditions adaptedto the production of gasoline boiling range products and thereafterblending the gasoline fractions of each of the hydrocrack-' ing andcatalytic cracking stages to form a motor fuel product.

Extensive study of the problem of converting high boiling petroleumcharge stocks into more useful gasoline boiling range materials hasindicated that the hydrocracking process is especially suitable foryielding a motor fuel boiling range product of high quality. Thetermhydrocracking is a descriptive term of the art which characterizes aconversion process in which the hydrocarbon charge stock, boiling abovethe gasoline boiling range and comprising a mixture of relatively longchain hydrocarbons containing 12 or more carbon atoms per molecule issubjected to reaction conditions in which the hydrocarbon components ofthe charge stock tend to undergo scission or cracking in the presence ofhydrogen at a superatomospheric pressure, any olefinic or aromaticcomponents involved in the process being simultaneously converted intotheir naphthenic and/or paraifinic analogs of substantially shorterchain length than the hydrocarbons comprising the charge stock andinvolved in the convere sion. The reaction is carried out in thepresence of a catalyst comprising a cracking component, usually anacid-actin g support, such as a calcined silica-alumina composite, and ahydrogenating component, usually a metal selected from the elements ofgroup VIII of the periodic table, such as palladium or platinum. It isalso known that the long chain aliphatic components of the charge stockmay be more conveniently or economically converted to shorter chainhydrocarbons boiling in the gasoline range by cracking thesehydrocarbons directly in the presence of a cracking catalyst, such asthe aforementioned silica-alumina composite. It has been found, however,that the aromatic components which generally accompany the aliphaticcompounds present in high boiling hydrocarbon feed stocks do not readilyundergo cracking reactions in the presence of a catalyst containing onlycracking components but, instead, are converted in large measure intocarbon and'light, non-condensable gases, such as hydrogen, methane,ethane, etc. The aromatic components, if separated from the feed stock,however, can be conveniently and economically converted into gasolineboiling range products in a separate hydrocracking reaction withoutsignificant production of carbon and/or light hydrocarbon gases. By thusseparating the and nitrogenous contaminants which comprises hydroc l iaromatic and aliphatic portions of the high boiling charge stock in apreliminary step, a process for handling such charge stocks wherebyoptimum yields and products of optimum quality boiling in the gasolinerange are obtained The present invention. provides a combination processwherein the separated alifrom each stage of the process.

These detrimental effects are usually evidenced by a marked reduction inthe catalytic activity of the cracking and hydrocracking catalysts,necessitating the use of. more severe conversion conditions in bothstages of the process. Accompanying such higher conversion temperatures,both stages of the process yield an excessive proportion of lighthydrocarbon gases which are the uneconomical end products of thecracking and hydrocracking reactions. bus, the presence of thenitrogenous and sulfur-containing contaminants in the feed stock rapidlyreduces the capacity of the catalyst to effect the desired crackingreaction, requiring the use of ever increasing temperatures in order toovercome the loss in cracking activity of the catalyst. The net effectof such nitrogen and sulfur-containing contaminants in the feed stock isa reduction in the net yield of the desired gasoline boiling rangeproduct from a given quantity of charge stock and the requirement ofmore frequent reactivation of the catalyst by virtue of the depositionof carbonaceous residues on the catalyst which accumulate and acceleratethe deactivation of the catalysts. In order to recover at least part ofthe activity of the catalyst the reactor must be shut down and thecatalyst removed or reactivated in place by passing through the catalystbed a stream of an oxygencontaining gas. These procedures necessitateadditional plant equipment and frequent costly interruptions of theprocess, as well as hastening the ultimate complete, irretrievabledeactivation of the catalyst.

in accordance with the present combination process, the nitrogen andsulfur-containing contaminants present in the high boiling feed stockare removed prior to the cracking and extraction stages of the processin a preliminary hydrorefining treatment wherein the charge stock,together with an atmosphere of hydrogen, is passed at hydrorefiningconversion conditions through a bed of catalyst of particularcomposition especially adapted to the conversion of the nitrogen andsulfur-bearing contaminants present in the feed stock into ammonia andhydrogen sulfide which can be separately removed in a treatmentpreceding the extraction stage of the present process.

The objective of the present combination of process steps, therefore, isto economically convert high boiling charge stocks derived frompetroleum and containing organically-bound nitrogen and sulfur compoundsinto an ultimate gasoline boiling range product of high quality formotor fuel use. Another object of this invention is to provide a meansof converting a high boiling hydrocarbon charge stock into a gasolineproduct and maxi: mizing such conversion.

In one of its embodiments this invention relates to a process forconverting a petroleum stock boiling above the gasoline range andcontaining aromatic components Patented Feb. 27, 1962 extract separatefrom a non-aromatic railinate, catalytically hydrocracking said aromaticextract in the presence of a catalyst containing hydrogenating andcracking catalyst components, catalytically cracking said railinate, andblending the gasoline boiling range fractions of the cracked andhydrocraclted products.v

Specific embodiments of this invention relate to particular processconditions and to specific methods of recycling certain fractions of theproduct, such as the residualbottoms of the hydrocracked product, afterseparation of the gasoline boiling range fraction from the hydrocrackedproduct, to the inlet of the hydrocracking stage or to the inlet of theextraction stage of the process.

The flow diagram of the process involved in the present invention isdiagrammatically illustrated in the accompanying drawing to whichreference is hereby made for further description of the invention. Thecharging stock to the present process, herein referred to generally as apetroleum fraction boiling above the gasoline boiling range fraction, ischarged into the process fiow through line 1 of the diagram. Typcial ofthe charge stocks boiling above gasoline are the so-called gas oilfractions which includes the upper end of the gasoline boiling rangefraction, kerosene, and the higher boiling cuts of petroleu 1., such asthe lubricating oil fractions having a top boiling range limit of about900 F. These charge stoc is may be derived from any suitable source,although highly aromatic and condensed ring hydrocarbon fractions areparticularly adapted for use as charge stock herein. In the event that astock boihngin the lube oil range is charged to the present process, itis desirably diluted with a relatively light parafiin diluent, such ashexane, heptane or a small amount of a gasoline boiling range fractionin order to reduce the viscosity of the stock, particularly during thestages of the process operated at relatively low temperatures.

The charge stock, together with hydrogen introduced through line 2,enter hydrorelining zone 3, containing a hydrorefining catalystmaintained at hydrorefining reaction conditions. Hydrogen at a pressurepreferably above 500. lbs. per square inch, up to about 3000 lbs. persquare inch, and more preferably from about 1000 to about 2000 lbs. persquare inch enters zone 3, at a rate equal to at least 500 standardcubic feet per barrel ofliquid' charge stock. The catalyst provided inzone 3-, is a supported hydrogenation catalyst comprising a metal ofgroup VIII of the periodic table, such as one of'the iron group metals,including nickel, cobalt or iron or one of the platinum group metals,such as palladium, platinum, iridium, or ruthenium on a supportconsisting of one or more refractory, inert metal oxides. The iron groupmetals are preferably combined with a metal or oxide of a metal selectedfrom group VI of the periodic table, preferably molybdenum in themetallic state or in the form of a compound of molybdenum. Therefractory metal oxide support for the hydrogcnating component of thecatalyst is an oxide inert in the reaction, such as'alumina, zirconia,thorium oxide, magnesia, mixed metal oxides such as alumina-zirconia,alumina-magnesia or a clay, in which the composition of the mixture ofoxides may be varied within rather wide ranges to provide operablecatalyst composites. The preferred metal oxide base is alumina. Thehydrorefining conversion provided in zone 3 is preferably eifected at atemperature within the range of from about 600 to about 900 F. and morepreferably from about 650 to about 800 F; The actual conditionsmaintained in zone 3 will depend to some extent upon the type ofnitrogenous compound contaminating the charge stock and. the diificultyencountered in converting this compound to free ammonia to the extentrequired to form a liquid reaction product containing less than about 5ppm. of total nitrog As previously indicated, the nitrogen content ofthe liquid portion of the hydrorefined product has a pronounced effectupon the, activity of the hydrocracking and cracking catalysts utilizedin the subsequent stages" of the process. Thus, it has been found thatby reducing the nitrogen content of the feed stock to the hydrocrackingand cracking stages of the process to less than 5 p.p.m. total nitrogen(from a nitrogen content in the charge stock of generally above about1500 ppm.) the cracking and hydrocracking stages may be operated forlong periods of time without regeneration of the catalyst and withoutsignificant reduction in the activity of the catalyst for the desiredcracking and hydrocracking purposes. It is therefore essential for theproper operation of the cracking and hydrocracking stages of the presentprocess that the nitrogen content of the liquid portion of thehydrorefined product be reduced to less than 5 p.p.m., and preferably toless than 1 ppm. in order to effect the cracking and hydrocrackingstages of the process with the accompanying aforementioned advantages.

The mixed phase reaction product of hydrorefining zone 3 is withdrawntherefrom through line 4, and discharged into separation zone 5 whereinthe normally gaseous and normally liquid portion of the hydrorefinedproducts are separated for further processing in accordance with thepresent invention. The mixture of gaseous and normally liquid productspresent in the product of the hydrorefining reaction charged intoseparation zone 5, is generally separated into a light, normally gaseousfraction comprising ammonia, hydrogen sulfide (formed by the reaction ofhydrogen with the sulfur compounds normally present in the feed stock),unconconverted hydrogen and light hydrocarbon gases, such as methane,ethane, etc. Ammonia may ordinarily be removed from the light gaseousfraction by washing the latter with a dilute aqueous solution of am'neral acid, such as sulfuric acid, or by passing the mixture of gasesover a cationic, ion-exchange resin, the ammonia being removed throughline 6, from zone 5. Hydrogen sulfide is generally recovered from therecycle hydrogen gas by solvent extraction with an organic solvent, suchas ethylene or diethylene glycol and removed from the process flowthrough line 7. The residual light gases, comprising generally a mixtureof hydrogen and methane, are recovered from the hydrogen sulfideextractor and desirably recycled to the hydrorefining zone, beingcharged into the inlet of the hydrogen stream thereto through line 8,connecting line 7 with line 2. The re maining light gaseoushydrocarbons, generally containing C to C paraffins, olefins anddiolefins, is removed fromseparation zone 5, through line 9, anddischarged from the process.

At the foregoing preferred hydrorefining reaction conditions, maintainedin the hydrorefining reaction zone 5 util'zing hydrogen at a highpressure and a catalyst which effects the hydrorefining conversion atrelatively low temperatures, the yield of undesired light gaseoushydrocarbons produced in the hydrorefining conversion is low and a largeproportion of the charge stock is retained as liquid, non cracked,paraffinic and naphthenic hydrocarbons.

. The normally liquid portion of the hydrorefined product, afterseparation of ammonia, light gaseous hydrocarbons, hydrogenand hydrogensulfide therefrom is re' traction procedure with either a liquid solventor a solidadsorbent which preferentially extracts the aromaticcomponents from the liquid hydrorefined stock. By

aoasnaa extraction is meant to include any form of separation procedurefor recovering aromatic components from a mixture of hydrocarbons,including extraction by adsorp tion of the aromatic hydrocarbons on asolid adsorbent, liquid-liquid solvent extraction, extractivedistillation, molecular'sieve separation, or urea or thioureaclatharation procedures. The wide variety of methods and proceduresutilized by the prior art for recovery of aromatic components fromliquid hydrocarbon mixtures are contemplated herein as suitableextraction methods and are within the scope of the term extraction asutilized herein. One of the preferred procedures, for separatelyrecovering the aromatic and non-aromatic hydrocarbon components of thehydrorefined product is the liquid-liquid solvent extraction processwherein the liquid portion of the hydrorefined product is contacted,preferably under countercurrent liquid-liquid flow conditions, in asuitable contacting tower with a solvent which is selec tively misciblewith the aromatic components of the feed stock, thereby producing a richsolvent streamcontaining the dissolved aromatic components of the feedstock and a separate non-aromatic rafiina'te phase which is removedoverhead from the solvent extraction zone and separately treated inaccordance with the process of this invention. The rafiinate removedfrom the extraction zone is desirably water-washed to remove thenormally small amount of solvent that dissolves in the hydrocarbonstream by virtue of the contact in the solvent extraction tower. Therich solvent stream comprising the aromatic components of the feed stockdissolved in the liquid phase solvent solution is removed from aromaticextraction zone 11, through line 12, into extract recovery zone 13,wherein the dissolved aromatic components of both monoand polycyclicstructure are recovered from v the rich solvent for example, bystripping. Most solvents utilized for solvent extraction purposes in therecovery of aromat c components from hydrocarbon stocks contain water,the stripping operation being primarily steam stripping which iseffectively accomplished by merely heating the rich solvent stream to atemperature above the boiling point of the rich solvent, Whileintroducing steam, if desired, into the bottom of the extract recoveryzone.

Another effective method of recovering components of the hydrocarbonfeed stock, pecially preferred when the charge stock is a viscous, highboiling point oil which is diluted with a light naphtha to reduceviscosity, is the method referred to as adsorption in which the stock ispassed through a stationary bed of solid adsorbent, such as silica gelpartcles or charcoal, the aromatic components being retained by theadsorbent and the non-sorbed raffinate passing through the column asefiluent. In the latter adsorption method, the extracted aromaticcomponents retained on the solid adsorbent are generally removedtherefrom by means of heat supplied to the extract recovery zone as thesensible heat of a heated inert gaseous desorbent or as a hot liquiddesorbent such as a light parafiin naphtha heated, for example, to aboveabout 100 R, up to 400 F.

The non-aromatc raflinate is recovered from extraction zone 11 throughline 14, the raffiuate efiluent being discharged into zone 15 whereinany residual solvent contained in the raftinate stream is removedtherefrom, for example, by distillation or by washing with water. Theraffinate thus recovered in zone 15 is dscharged therefrom through line17.

Suitable solvents for use in the aromatic extraction zone may beselected from a wide variety of organic compounds, such as the alcohols,the glycols, the polyglycols, the phenols, the amines, the ethers, etc.One of the preferred solvents for aromatic extraction is an aqueoussolution of a polyglycol, such as diethylene or triethylene glycol, withor without added quantities of dipropylene or tripropylene glycol inadmixture therewith the aromatic a method csand containing from 1.0 toabout 15 percent by weight of water.

In accordance with the process herein provided, the aromatic extractrecovered from the hydrorefined feed stock is separately subjected tohydrocracking and the parafiinic raifinate portion of the hydrorefinedfeed stock is separately subjected to catalytic cracking, each of thereactions being effected in separate zones in order to obtain maximumconversion of each of the fractions to gasoline boiling range productsof high quality for motor fuel use. Hydrocracking of the aromaticextract, however, is feasible only if and when the nitrogen-containingcontaminants present in the original charge stock and inherentlytransferred into the aromatic extract during the extraction stage, areremoved prior to the extraction stage to a nitrogen level less than 5ppm. The hydrorefining stage ofthe present combination process isdesigned, when operated at'sufiiciently severe conditions,

to convert all of the nitrogenous compounds originally present in thefeed stock into ammonia which when stripped from the hydrorefined stockwill reduce the total nitrogen content of the stripped stock to lessthan 5 ppm. of nitrogen. Only when the nitrogen content of the feed tothe hydrocracking step is reduced to 5 ppm. or less will the catalystused in the hydrocracking step remain active for a sufilcient period ofon-stream use to be practically feasible.

Hydrocracking is effected in zone 18 in the presence of a catalystcomprising a cracking component and a hydrogenating component, bothcomponents of the catalyst acting simultaneously to etfect the intendedconversion. Suitable hydrocracking catalysts contain from about 0.5 toabout 15 percent by weight of the hydrogenating component, selected fromthe metals, sulfides and oxides of the elements of group VIII of theperiodic table, particularly nickel and/or cobalt, composited with acracking catalyst base and preferably containing from about 4 to 20percent by weight of molybdenum or a molybdenum compound such as themolybdate or thiomolybdate salts of the iron group metal. Other groupVIII metals suitable as the hydrogenating compounds of the hydrocrackingcatalyst are platinum, palladium and ruthenium which are present in thecatalyst in amounts of from about 0.01 to about 5 percent by weight,composited with the cracking catalyst base. The base may consist of acomposite of silica-alumina, silica-zirconia, silica-alumina-zirconia,alumina-b-oria, silica-magnesia or an alumina support containing from0.1 percent to about 5 percent by weight of combined halogen, selectedfrom either or both fluorine and chlorine. It has been found throughcomparative tests of various catalysts that one of the preferredhydrocracking catalysts is a composite of palladium on a crackingcatalyst base consisting of silica-alumina and containing from about 0.2to about 0.8 percent by weight of palladium.

In the hydrocracking stage of the process, the aromatic extract at atemperature of from about 600 F. to about 900 F., together with hydrogenat a pressure of from about 500 lbs. to about 3000 lbs. per square inchis passed into hydrocracking zone 18, containing the hydrocrackingcatalyst at a space velocity of from about 0.2 to about 2.5 volumes ofliquid feed stock per volume of catalyst per hour. At the indicatedreaction conditions and particularly, when the residence time of thearomatic extract with the hydrocarcking catalyst in zone 18 issufficient, the aromatics undergo hydrogenation and at substantially thesame time, the resulting ring compounds split into smaller molecularweight fragments of aliphatic structure, boiling within the gasolineand/or kerosene range, constituting the desired end products of thepresent process.

The mixed phase product of the hydrocracking process is removed fromzone 18 through line 19, into separation zone 20 wherein the lightgaseous portion of the product is separated into the desired fractions,for example, by

hydrogen supply line 23 which feeds into hydrocracking zone 18. Thefraction of the hydrocracked products boiling above the butanes, up toabout 400 1 comprising gasoline boiling range material, one of thedesired end products of the process is removed from zone through line 24into line 25 leading to product blending and storage. A fraction boilingabove the end point of the gasoline fraction comprising terosene andfuel oil fractions may be separately recovered for jet fuel use orrecycled in the process and subjected to further hydrcracking or solventextraction, as desired. The latter fraction is removed from separationzone 20 through line 26- and either discharged from the process asproduct through line 2?, diverted from line 26 into line 28, which inturn connects with line is, feeding into hydrocracliing zone 18, orconveyed by line 26 into line leading into aromatic extraction zone i1wherein the aromatic components normally present in the bottoms fractionof the hydrocracking products are recovered therefrom by the presentsolvent extraction step.

Referring again to the raflinate portion of the extraction stage,removed from zone through line 17, this predominantly parafiinicfraction is subjected to catalytic cracking in zone 29 in the presenceof an acidic cracking catalyst which ruptures the long chainhydrocarbons present in the rafiinatc fraction into smaller fragmentsboiling within the gasoline or kerosene range, depending upon theparticular temperature and pressure conditions maintained in thereactor. Cracking zone 29 contains a cracking catalyst distributedtherein, in fixed bed, fluidized, or moving bed relationship to theincoming charge. The rafiinate charge is catalytically cracked in zone29 by passing the raffinate at a temperature of from about 750 to about1100 F., and more preferably at a emperature of from about 800 to about1000 F. into contact with the cracking catalyst at a pressure of from 10to about 1000 lbs. per square inch and at a rate equivalent to a liquidhourly space velocity of from about 0.5 to about 2.5 volumes of liquidfeed stock per volume of catalyst per hour. Fluidizcd catalytic crackingis generally the preferred method of contacting the catalyst with thecharge stock and preferably at temperatures of from about 8' to about1000" F. and at pressures of from about 10 to about 100 p.s.i.g.

Suitable cracking catalysts are Well-known in the art, includinggenerally certain acid-acting composites of refractory metal oxides,such as silica-alumina, silica-zirconia, silica-magnesia, alumina-boria,alumina-silica-magnesia, siliea-alumina-zirconia and other acid-actingmixtures of refractory metal oxides containing from about 2 to aboutpercent by weight of silica and/ or boria.

Although the product of the cracking reaction in the case of the presentraifinate stock is primarily a liquid material boiling in the gasolinerange, certain gaseous products are also likely to be formed, such asthe low molecular weight hydrocarbon gases, including methane, ethane,propylene, and the butanes. In order to separate the various fractionsof the catalytically cracked product, the reaction effluent from zone 29is passed through line 30 into separation Zone 31 wherein the desiredfractionation and separation is effected. A light, normally gaseousoverhead is fractionally distilled from the catalytic crackingreactionproduct in zone 31, being removed therefrom through line 32 anddischarged from the process. A gasoline boiling range fraction,including the components boiling above C ,-up to about 400 F. end pointis separated in zone 31 as an intermediate boiling range fraction whichis removed through line 33 and discharged into line 25 for blending toform the gasoline product of the present process.

The bottomsresidue boiling above the 400 F. end point of the desiredgasoline fraction is separated from the cracked products in zone 31 andrecycled through line 3d to the inlet of hydrocracking zone 18, line 16.The high boiling residual bottoms recovered from the catalyticallycracked products, is generally rich in arcmatic and olefinichydrocarbons and is a suitable feed stock to the hydroerackingzone. Inthis manner, the initial feed-stock in its entirety is converted intothe desired gasoline boiling range product.

The present invention is illustrated with respect to several of itsspecific embodiments in the following ex-- the scope of the inventionnecessarily in accordance 7 to the cracking reactor.

therewith.

Example I A Mid-Continent virgin gas oil stock, having a boiling rangeof from about 560 F. to about 930 F. containing 31 percent by weight ofpolynuclear aromatic components and 1200 ppm. of nitrogen asnaturally-occurring nitrogenous contaminants is catalytically cracked,using an alumina-silica cracking catalyst containing 12 percent byweight of silica. In this run, the charge stock, at a pressure of 900lbs. per square inch and at a temperature of 875 F. is charged into afixed bed of the.

cracking catalyst at a space velocity of 1.5 volumes of iquid charge pervolume of catalyst per hour. The normally liquid portion of the productsis fractionated to separate a gasoline boiling range fraction having anend boiling point of 400 F. from a liquid bottoms residue (23 percent byvolume of charge) which is recycled The net conversion to gasolineboiling range product is about 62 percent by weight of the materialcharged, 8 percent by weight of the original feed is separated as aliquid tar from the distillate bot-v toms and about 3450 s.c.f./bbl. ofcharge, consisting of light, non-condensable gaseous hydrocarbons andhydrogen are produced in the conversion. The catalyst re-.

quires regeneration after 56' hours on stream and replacement afitertwo-regenerations.

In the following run the identical charge stock speci-v ficd in theabove catalytic cracking run is first subjected to hydrorefining bypassing the charge stock, together with hydrogen (2000 standard cubicfeet per barrel of charge stock) and at a pressure of 3000 lbs. persquarev inch gauge over a hydrorefining catalyst consisting of 2 percentby weight of nickel, 12 percent by weight of molybdenum and'3 percent byweight of cobalt on an alumina base, the catalyst being maintained inthe hydrorefining zone as a fixed bed of precalcined pellets. The chargestock is passed through the hydrorefining catalyst at a temperature of725 F. and at a liquid hourly space velocity of 0.5 volumes of liquidper volume of catalyst per hour. The exit gas from the top of thereactor contains substantially all of the ammonia formed during thehydrorelining conversion and is passed through a countercurrent acidwash stream to remove the ammonia. hydrorefined products is stripped atatmospheric pressure to remove the normally gaseous hydrocarbons fromthe liquid portion of the product; 51 s.c.f. of gaseous.

hydrocarbons per barrel of charge stock is separated. The conversionresults in a net consumption of hydrogen.

The stabilized liquid portion of the hydrorefined prodnot is thereaftersubjected to extraction for the removal of aromatic components bypassing the liquid product The liquid portion of the.

begin to appear in the efiluent stream, 'the feed stock is diverted to asecond adsorption tower containing reactivated silica gel adsorbent. Thefirst tower is thereafter reactivated and the aromatic components of thecharge stock recovered from the adsorbent by passing a paraffinicnaphtha boiling from about 300 to about 350 F. downwardly through thecolumn of spent adsorbent at a temperature of about 300 F. and removingthe efiluent in liquid phase from the bottom of the adsorption tower.The desorbed efiiuent is thereafter fractionated to recover the aromaticcomponent as bottoms from the liquid efiluent and to distill overheadthe paraffinic naphtha desorbent.

As soon as aromatic components begin to appear in the eflluent of thesecond column, a similar desorption is carried out on the second columnas fresh hydrorefined charge stock is charged into the first adsorptioncolumn. Aromatics are recovered from the liquid portion of thehydrorefined product in this manner to provide a yield of 31 volumepercent of the hydrorefined product. The aromatics thus recovered arereserved for use in the subsequent hydrocracking stage of the process.The nitrogen content of both the raiiinate and extract portions of thehydrorefined product is reduced to less than 0.5 ppm. total nitrogen.

The rafiinate portion of the hydroreiined product (adsorber eluate) iscatalytically cracked in a separate fluidized catalytic cracking reactorcontaining a silica-alumina cracking catalyst (containing 12 percentsilica). The rafiinate preheated to 930 F. and at a pressure of 900lbs./in. is charged at a rate of 1.3 liquid hourly space velocity intothe fiuidized bed of cracking catalyst. The products of the crackingreaction are first stripped at the reactor pressure and thereafterfractional'ly distilled, separating a light normally gaseous overheadfrom the cracked products, (1090 s.c.f./bbi. of charge), an intermediategasoline fraction boiling up to 400 F. end point (68 percent by weightof the charge) from the remaining liquid portion of the product and aliquid bottoms residue (21 percent by weight of the initial rafiinateout) which is thereafter mixed with the aromatic extract recovered fromthe hydrorefined product and charged to the hydrocracking reactorhereinafter described. The gasoline boiling range cut is reserved forsubsequent blending with the similar boiling range cut of thehydrocracking reaction product.

The mixed liquid bottoms of the cracking reaction product and thearomatic extract recovered from the adsorber are charged into ahydrocracking reactor at a liquid hourly space velocity of 0.8 volumesof liquid/ volume of catalyst/hour, together with hydrogen at a rate of1000 standard cubic feet per barrel of charge stock at a pressure of3000 lbs/in. and at a temperature of 725 F. The hydrocracking catalyst,consisting of 0.4 percent palladium on a silica-alumina crackingcatalyst base, is maintained as a fixed bed in the reactor. Thehydrocracking conversion products are first passed into a high pressureseparation zone wherein the noncondensable gases are separated from thecondensed liquid portion of the product at the particular pressuremaintained in the hydrocracking reaction zone. The non-condensable gasfraction, consisting mostly of hydrogen, is recycled to thehydrocracking zone. Thereafter, the light hydrocarbon gases, up to andincluding nbutane, are separated from the liquid portion of the highpressure condenser. An intermediate cut boiling from C to 400 F. andpoint is separated from the hydrocracked products and reserved as thegasoline boiling range fraction for blending with the gasoline productof the catalytic cracking zone. The gasoline boiling range fraction ofthe hydrocracked product represents 10' a conversion of 78 percentbasedupon the charge stock to the hydrocracking reactor. The liquidbottoms fraction representing the material of the hydrocrackedprodnotboiling above the end point of gasoline and containing 21 percent by"weight of aromatic components is recycled to the inlet of the aromaticextraction zone hereinbefore referred to. The hydrocracking zone,operated at the above conditions, is capable of on-stream use for aperiod of over 800 hours before the conversion falls below 75 percent;thereafter the temperature of the hydrocracking zone may be increased anadditional 25 F. to restore the catalyst to its initial conversion rate.In this manner the hydrocracking catalyst may be continuously utilizedfor the hydrocracking conversion for a period of over 4000 hours beforereactivation is required.

The net conversion of the virgin gas oil feed stock to gasoline boilingrange product is over 89-percent and the product has a clear octanenumber of 90.3.

I claim as my invention:

1. A process for converting a petroleum stock boiling above the gasolinerange and containing aromatic components and nitrogenous contaminantswhich comprises hydrorefining said stock in the presence of ahydrorefining catalyst at a temperature, pressure and time of contact ofthe'stock with the catalyst sufficient to convert the nitrogen of saidnitrogenous contaminants into ammonia, removing ammonia rom the liquidportion of the hydrorefined stock to a nitrogen content notsubstantially in excess of 5 p.p.m., extracting the aromatic componentsfrom said liquid hydrorefined stock and recovering an aromatic extractseparate from a nonaromatic raifinate, catalytically hydrocracking saidaromatic extract in the presence of a catalyst containing hydrogenatingand cracking catalyst components, catalytically cracking said raffinateand separating from the resultant products a fraction boiling in thegasoline range and a heavier residual fraction rich in aromatic andolefinic hydrocarbons, supplying said residual fraction to thehydrocracking step, and blending the gasoline boiling range fractions ofthe cracked and hydrocracked products.

2. The process of claim 1 further characterized in that said aromaticextraction is effected in the presence of a solid adsorbent for aromatichydrocarbons and said aromatic extract is recovered from the solidsorbent.

3. The process of claim 1 further characterized in that said crackingcatalyst component of the hydrocracking catalyst is a composite ofsilica and alumina.

4. The process of claim 3 further characterized in that saidhydrogenating component of said hydrocracking catalyst is palladium.

5. The process of claim 1 further characterized in that saidhydrorefining catalyst comprises a metal of group VIII of the periodictable composited with a base comprising alumina.

6. The process of claim 5 further characterized in that said group VIIImetal is selected from the group consisting of nickel and cobalt andsaid catalyst base is alumina containing a molybdenum compound.

7. The process of claim 1 further characterized in that saidhydrorefining reaction is elfected in the presence of hydrogen and at apressure of from about 1000 to about 3000 lbs. per square inch, atemperature of from about 650 to about 850 F. and a liquid hourly spacevelocity of from about 0.5 to about 1.5 volumes of liquid hydrocarboncharge stock per volume of catalyst per hour.

8. The process of claim 1 further characterized in that the liquidportion of the hydrocracked product is separated into a gasoline boilingrange fraction and a residue boiling above said gasoline boiling rangefraction and recycling said residue to the aromatic extraction stage ofthe process.

9;. The process of claim 1 further characterized inthat the, residuefrom the liquid precinct of the hydro cracking reaction is. recycled tothe inlet of the hydrocraekingstep, mixed with said extract of the,aromatic extraction step, and the resulting combined feed charged 5 intothe hydrocracking reaction. v

References Cited in the file of this patent UNITED "STATES PATENTSGleirn Sept. 22, 1959

1. A PROCESS FOR CONVERTING A PETROLEUM STOCK BOILING ABOVE THE GASOLINERANGE AND CONTAINING AROMATIC COMPONENTS AND NITROGENOUS CONTAMINANTSWHICH COMPRISES HYDROREFINING SAID STOCK IN THE PRESENCE OF AHYDROREFINING CATALYST AT A TEMPERATURE, PRESSURE AND TIME OF CONTACT OFTHE STOCK WITH THE CATALYST SUFFICIENT TO CONVERT THE NITROGEN OF SAIDNITROGENOUS CONTAMINANTS INTO AMMONIA, REMOVING AMMONIA FROM THE LIQUIDPORTION OF THE HYDROREFINED STOCK TO A NITROGEN CONTENT NOTSUBSTANTIALLY IN EXCESS OF 5 P.P.M., EXTRACTING THE AROMATIC COMPONENTSFROM SAID LIQUID HYDROREFINED STOCK AND RECOVERING AN AROMATIC EXTRACTSEPARATE FROM A NONAROMATIC RAFFINATE, CATALYTICALLY HYDROCRACKING SAIDAROMATIC EXTRACT IN THE PRESENCE OF A CATALYST CONTAINING